In the U.R.F game mode (available in April 2014), Alistar was deemed overpowered/obnoxious, and was ultimately disabled in non-custom games.

Quotes

Alistar's quote "Mess with the bull and you get the horns!" may be a reference to the Breakfast Club. Said by principal Richard Vernon: Don't mess with the bull, young man. You'll get the horns. [1] A side-by-side comparison can be seen here.

In his Chinese artwork, Alistar has four fingers despite his model only having three. It also shows him having three knuckles (suggesting four fingers) in his classic, black and golden artwork. This mistake is corrected in the Matador Alistar, Unchained Alistar, Longhorn Alistar and Chinese Golden Alistar artworks.

In his Original Splash Arts, some show him with 4 fingers, while others display the correct 3 fingers.

In his Chinese Longhorn Alistar and Classic arts, he still has 4 fingers.

There was originally a bug that the Longhorn Alistar texture would all turn blue, this was however later fixed.

In early 2012, Alistar's Classic artwork was replaced by the Chinese Classic skin artwork, as well as those of Fiddlesticks, Galio, and Malzahar. These were the first in a long line of many champions to get new artworks on future patches.

The skin is free and obtainable by visiting the Riotgamesinc channel on YouTube and then syncing with the appropriate LoL website. If you do not have the champion, Alistar will be given to you for free along with the said skin.